Collaborative Research: Pacing and Pathways of Carbon Sequestration in a warm Pliocene Ocean

Oceans play an important role in the climate system, having already taken up around one-third of anthropogenic carbon released into the atmosphere since the Industrial Revolution. However, as temperatures continue to climb, the extent to which oceans will continue to mitigate rising atmospheric carbon remains to be fully constrained. Yet quantifying this atmospheric carbon sink is critical to projecting the future response of the climate system. To narrow this gap, researchers in this study are investigating changes in carbon uptake and storage in the Pacific Ocean during the Pliocene, an interval of warmth around 3 million years ago that is commonly used as an analog to investigate the response of the climate system to modern warming. Using both data and models, the aim of this study is to quantify the marine carbon response to two specific temperature-sensitive mechanisms within the ocean with the goal of better predicting carbon storage during future warmth. This collaborative project is also advancing public understanding of climate science through the development of a new exhibit for the Central Gallery of the Yale Peabody Museum showcasing how climate signals are measured from fossil plankton in ancient oceans. Additionally, the project is supporting participation in George Mason’s Summer Undergraduate Research Experience (S.U.R.E) Program, doctoral students at Yale and Mason, and engaging high school and undergraduate students in the translation of core science into a publicly accessible display During warm climate conditions, such as the Pliocene, marine carbon cycling was likely affected by changes in circulation and temperature-dependent rates of biological processes. Changes in these levers are predicted to have cascading effects on the relative amount of short- and long-term marine carbon storage, and through subsequent feedbacks, the climate system as a whole. Although both circulation and temperature-dependent biology have been argued to dominate carbon cycle changes in warm climate states, they have yet to be directly compared in state-of-the-art climate models and model-data comparisons. This study addresses this gap using a series of Community Earth System Model experiments designed to examine each lever individually, and in combination, to quantify the associated model-predicted changes in carbon storage. These predictions are also being tested in the Pliocene using geochemical proxy data for ocean pH, dissolved inorganic carbon, and temperature at four Pacific Ocean sites. This study provides a valuable assessment of the potential strength and interaction of circulation and temperature-dependent remineralization on marine carbon cycling and serves as a testbed for how well climate models simulate carbon cycling and other key elements of ocean biogeochemistry. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.